1. Field of the Invention
Embodiments of the invention generally relate to an electronic test system for large substrates. More particularly, embodiments of the invention generally relate to an electron beam test system for large glass panel substrates.
2. Description of the Related Art
Active matrix liquid crystal displays (LCDs) are commonly used for applications such as computer and television monitors, cell phone displays, personal digital assistants (PDAs), and an increasing number of other devices. Generally, an active matrix LCD includes two substrates, such as two glass panels for example with a layer of liquid crystal materials held therebetween. One of the substrates typically includes a conductive film formed thereon. The other substrate typically includes an array of thin film transistors (TFTs) coupled to an electrical power source. Each TFT may be switched on or off to generate an electrical field between a TFT and the conductive film. The electrical field changes the orientation of the liquid crystal material, creating a pattern on the LCD.
The demand for larger displays, increased production and lower manufacturing costs has created a need for new manufacturing systems that can accommodate larger substrate sizes. Current TFT LCD processing equipment is generally configured to accommodate substrates up to about 1.5×1.8 meters. However, processing equipment configured to accommodate substrates sizes up to and exceeding 1.9×2.2 meters is envisioned in the immediate future. Therefore, the size of the processing equipment as well as the process throughput time is a great concern to TFT LCD manufacturers, both from a financial standpoint and a design standpoint.
For quality control and profitability reasons, TFT LCD manufacturers are increasingly turning toward device testing to monitor and correct defects during processing. Electron beam testing (EBT) can be used to monitor and troubleshoot defects during the manufacturing process, thereby increasing yield and reducing manufacturing costs. In a typical EBT process, TFT response is monitored to provide defect information. For example, EBT can be used to sense TFT voltages in response to a voltage applied across the TFT. Alternatively, a TFT may be driven by an electron beam and the resulting voltage generated by the TFT may be measured.
During testing, each TFT is positioned under an electron beam. This is accomplished by positioning a substrates on a table positioned below the beam and moving the table to sequentially position each TFT on the substrate below the electron beam test device. As substrates increase in size, so does the table and associated equipment used for the testing. Larger equipment requires more space, i.e., a larger footprint per processing unit throughput, resulting in a higher cost of ownership. The large size of the equipment also increases the costs associated with shipping and may, in some cases, restrict the means and locales to which such equipment may be transported.
There is a need, therefore, for a compact testing system for large substrates that requires less clean room space and that can reliably position large substrates under an EBT device.